Whenever Byron Lindsley Jr. identified a threat to the environment, he took it personally  as if developers were encroaching on his own back yard.

As the founding director of the Mountain Defense League in 1973, he rallied thousands of people to his cause: preventing residential developments at Middle Peak in the Cuyamacas and in the Kemp Ranch area of the Lagunas.

Until his health began to fail in recent months, Mr. Lindsley kept up the fight from the desert to the coast, spending as much time in meetings and court hearings as in his beloved East County mountains.

"I had to leave the mountains to help save them," he told The San Diego Union-Tribune 10 years ago.

Mr. Lindsley, beset with high blood pressure and heart problems, was found dead Feb. 4 in his La Mesa apartment. He was 60.

The cause of death apparently was a stroke, said his brother, Philip, a San Diego attorney.

The son of a retired Superior Court judge, Mr. Lindsley brought the savvy of a layman's lawyer and the sensitivity of a lifelong conservationist and naturalist to the MDL, colleagues said.

"Backcountry conservation was where Byron's heart was," said Pandora Rose, who succeeded him as MDL director. "He was very good at generating interest and getting people involved."

Mr. Lindsley's grass-roots movement picked up steam after successfully opposing development on Middle Peak and Kemp Ranch. Subsequently, the MDL lobbied for the inclusion of 1,000 acres at Middle Peak to be absorbed by Cuyamaca Rancho State Park and the inclusion of the Laguna Meadows area into the Laguna Recreation Area.

"The Cuyamaca issues changed land-use law in the state," Mr. Lindsley told The San Diego Union in 1988, referring to a state Supreme Court ruling that the Environmental Protection Act must be applied to private as well as public lands.

Although Mr. Lindsley earned income over the years for environmental consulting, his primary professional career was in the service industry. He worked as an usher at the Del Mar Fair, Del Mar Racetrack and at San Diego Padres games in Qualcomm Stadium. He also served on the board of directors of Service Employees International Union local 2028.

"Byron knew as much about the legal processes as an environmental lawyer," his brother said. "He networked with experts in archaeology, astronomy, geology and ground-water specialists. Then he would pull everything together and present an environmental report."

His campaigns were successful in blocking a federal prison and Job Corps center project atop Mount Laguna and in heading off several development proposals for Palomar Mountain.

"You can't protect everything in the private-land system that we have," he said in 1993. "We've concentrated on preserving areas that are clearly unique, of high value and could set a significant precedent."

Mr. Lindsley was born in Washington, D.C., where his father had moved the family from San Diego while he pursued a master's degree and law studies at Georgetown University.

The Lindsley family returned to San Diego five years later. Mr. Lindsley graduated in 1960 from Crawford High School and went on to earn a bachelor's degree in sociology at the University of Oregon.

He joined the Sierra League in 1972 and served as its historian and as a chairman of many of its committees. Last spring, he was honored for his 30 years of service to the Sierra Club, which included rallying its members to support his conservation causes.

The Mountain Defense League is planning a tribute hike for Mr. Lindsley later this year in the Laguna Mountains. Donations are suggested to the Mountain Defense League or local chapters of the Sierra Club or Audubon Society.